Instruments subject to the made affirmative procedure are signed into law before being laid in Parliament but require approval from Parliament within a specified period. There are different types of made affirmative SIs: the most common type of made affirmative SI comes into force before it is approved (and can come into force before it is laid) but cannot remain in force unless it is approved by Parliament within a specified period. Another rarer type of made affirmative SI is laid after being made but cannot come into force unless the instrument is approved by Parliament. The relevant procedure and the length of the approval period is defined in the parent Act.